The present invention generally relates to the removal of contaminants or debris from a flowing liquid stream. The present invention more specifically relates to various embodiments of an apparatus which employs a filter media comprised of particulate filter matter in which the filter media may be backwashed to clean the captured contaminants from the filter media.
Removal of contaminants or debris from a flowing liquid stream by the employment of a filter media comprised of particulate filter material is known. Various prior U.S. patents teach the advantages of using various different sizes of various different particulate filter material. Many of the described filter systems require that the filter media be removed from the filter vessel each time it becomes necessary to scrub the contaminant from the media, thereby enabling the media to be used many times.
As stated in U.S. Pat. No. 4,496,464 (the “'464 patent”) these prior art systems require a considerable amount of additional space, and complicated plumbing must be connected between the various pumps, valves, and other mechanical members in order to interconnect the scrubbing vessel and filtering vessel so that various different predetermined flow patterns are attained. A substantial amount of equipment is required in order to return the filter media to the filter vessel. In addition to the added cost and the required additional space considerations, all of the external plumbing presents a continued maintenance problem; and, the numerous additional mechanical connections involved therein greatly increase the likelihood of leakage occurring from the different components of the filter system.
The '464 patent, which is incorporated herein in its entirety by this reference, provides additional explanation of the problems associated with filter systems which required transfer of the filter media from the filter vessel into a scrubber vessel. In an effort to solve these problems, the '464 patent discloses a filter system wherein the filter media remains within the filter vessel for the entire life of the media, and wherein the filter media is scrubbed or rejuvenated without removing the filter media to a second vessel.
One drawback of the apparatus disclosed in the '464 patent is that the entire interior of the separator vessel is continually subjected to higher pressure during the scrubbing cycle imposed by the scrubbing pump. As noted in the example described in the '464 patent, the initial pressure drop across the filter media may change from a low of 3-5 psi to a pressure drop of 15-25 psi 18 hours later, at which time the scrubbing cycle is initiated. During the scrubbing cycle, the pressure at the discharge nozzle must be sufficiently high to force the liquid into a guide means and to the bottom of the vessel, setting up a flow pattern in which the filter media is “intimately admixed with the liquid contained in the vessel” such that the flow follows a geometrical flow path which is in the form of a toroid having a central vortex which coincides with the axial centerline of the vessel. Achieving this flow pattern requires the repeated application of pressures during the scrubbing mode which are typically higher than the pressures to which the vessel is exposed during the filtering mode. As stated above, for the example provided in the '464 patent, this cycle is repeated approximately every 18 hours, such that the vessel is subjected to a continual stress cycle in which the maximum pressure may substantially exceed the normal operating pressure of the vessel during the filtering cycle. In addition, during the scrubbing cycle, the interior scrubber of the '464 patent is subjected to exterior forces for which the interior scrubber must be designed to resist collapse.
It should be further noted that the apparatus disclosed in the '464 patent has screens at the bottom of the vessel through which the filtered liquid is discharged to an outlet header. It should be appreciated that the lower screens can be subjected to very high loads. If the backwash pump comes on while the separator vessel is already at a relatively high pressure, the vessel pressure can increase by 25 psi or more. The lower screens are thus subjected to the increased pressure, as well as the hydrostatic pressure of the fluid in the separator vessel and the media bed overlying the lower screens. Therefore, when the backwash pump comes on, the lower screens can be exposed to relatively high transient loads, which have, with the prior art designs, resulted in catastrophic damage to the lower screens.